Um, I don't usually have the problem with my characters changing sides but they never behave the way I want them to. My probably-Nano plot undertook some really wild revisions this summer.
I think she's too boring good. She switched back to the used-to-be-evil category.
I figured out a way (involving bribes and threats) to make it work. I don't like that she gets one of my favorite characters killed, though. *sigh* But it has to happen. A lot of other stuff hinges on that.
What remains to be seen is what side she takes once she gets her bearings back.